Deposition of tungsten-containing materials using chemical vapor deposition (CVD) techniques is an integral part of many semiconductor fabrication processes. These materials may be used for horizontal interconnects, vias between adjacent metal layers, contacts between a first metal layer and the devices on the silicon substrate, and high aspect ratio features. In a conventional deposition process, the substrate is heated to the process temperature in a deposition chamber, and a thin layer of tungsten-containing materials that serves as a seed or nucleation layer is deposited. Thereafter, the remainder of the tungsten-containing film (the bulk layer) is deposited on the nucleation layer. Conventionally, the tungsten-containing bulk layer is formed by the reduction of tungsten hexafluoride (WF6) with hydrogen (H2). Tungsten-containing layers are deposited over an entire exposed surface area of the substrate including features and a field region.
Depositing tungsten-containing materials into small and, especially, high aspect ratio features may cause formation of seams inside the filled features. Large seams may lead to high resistance, contamination, loss of filled materials, and otherwise degrade performance of integrated circuits. For example, a seam may extend close to the field region after filling process and then open during chemical-mechanical planarization.